This invention relates to a web coating or printing apparatus and particularly to a web coater for applying a thin film of material onto an elongated web. The invention is also directed to a method of applying a coating based on such apparatus.
Many applications require a web member having a coating applied to one face. The recording and copying fields often use a web or tape like member having a coating on the face thereof. In the manufacture of the coated web, a large roll of the web material is formed for subsequent application of the coating. The web is fed from the roll through a coating apparatus which is specially constructed to deposit a thin film of the coating onto the web, with the coated web subsequently processed such as rewound for subsequent processing into retail sized tapes or other suitable products. The specification for certain products require a uniform coating of constant thickness which in turn requires highly accurate monitoring of the coating process. This is particularly true in those applications where the coating material is a relatively expensive material. For example, a silconecoated web is a typical example where the cost of the silcone coating material is a signficant part of the final product cost. As a result, silicone coating is applied to the web using highly precision formed apparatus such as a gravure coating apparatus. The gravure applicator may use an offset construction or alternatively a direct imprinting construction. The particular method will of course be dictated by the specifications in accordance with well-known procedures. Generally in such applications, the apparatus is set up by the operator to apply a coating of a certain thickness. A piece of the coated web is withdrawn, the coating removed and weighed to determine the accuracy of the application. This provides a reasonably quick determination of the quantity of material being deposited. The thickness of the coating may of course vary substantially from one specification to the next, depending upon the application, the materials of the web and coating and other factors known to those in the art. The apparatus should therefore provide for convenient adjustment of the thickness, preferably with the machine in operation. Finally, with the alternate method of application, a single machine which can be readily converted between an offset construction and a direct gravure construction would be highly desirable for purposes of minimizing the fixed machine cost to the coater company. In both instances of course, the necessary precision construction as well as adjustable features should be maintained in order to provide satisfactory low cost coating of the web.